This page contains information and resources for participants of our visitor survey in the GYE. You can find a copy of the Research Participant Information Sheet below, along with more information about climate change and forest disturbance in the GYE and the western United States. When we analyze results, give talks, or publish articles relating to the survey, we will post updates here, so check back occasionally if you would like to stay in the loop! Feel free to browse the rest of the Turner Lab website but note that you can only reach this tab through the link you were given.
Forests, Fire, and Climate Change – What is happening in the West?
There have been few summers recently without headlines of large wildfires in western North America. Even though fire is natural, something is different about recent fires. Here is a summary of fire ecology, with a focus on western forests, and the changes we are seeing around us.
What has fire been like historically?
Fire is a normal and often essential component of many North American ecosystems, from groundfires in longleaf pine savannahs of the southeast to stand-replacing forest fires here in the Greater Yellowstone Area. The types of fires we observe in different ecosystems vary just as the types of trees vary in forests across the country. Species within an ecosystem have many unique adaptations that help them persist, and even thrive, with fire.
Ecologists broadly distinguish between two different fire systems, one where the occurrence of fire is limited by available fuel and one where the occurrence of fire is limited by climate. Fire in the Greater Yellowstone Area has historically been climate limited, with warm and dry conditions suitable for large fires occurring every 100 – 300 years, on average. We know this in part from tree ring studies – in the 1980s, scientists collected samples from trees whose trunks showed evidence of past fires. The part of the trunk that burned will be scared by fire, but the remainder of the tree kept growing, adding a growth ring for every year since the fire. By counting the rings that grew since the last fire, we can determine how many years have passed between fire events. This method works for the past few hundreds of years that are within a single tree’s lifespan. Beyond this time period, for example over the last millennia, scientists collect lake core samples. Over thousands of years, pollen from nearby trees sinks to the bottom of a lake, and so does charcoal when forests burn. Layers of pollen and ash accumulate in the lake, allowing scientists to determine the frequency of fire based on the layers in the lake sediment.
In this climate-limited fire system of the Greater Yellowstone Area, lots of fuel is available to burn, but it rarely gets warm and dry enough for a fire to burn. Once it does, fires ignite naturally following lightning strikes and burn the forest canopy, including needles and small branches, as well as needles and smaller woody material on the ground. These fires are “stand-replacing” because they kill the old stand of trees and replace it with a new cohort of young trees. After a fire, there is a distinct mosaic, or patchwork resembling a stained-glass window, of unburned areas with living trees and burned areas with standing dead trees. Tree species in the Greater Yellowstone Area have different strategies to reestablish right after a fire. Some lodgepole pines have serotinous cones – this means their cones are “glued” closed with a wax that melts during a fire, releasing a rain of seeds right where it burned. Other tree species, such as Engelmann spruce, rely on wind to move their seeds from living trees to nearby burned areas.
In fuel-limited fire systems, climates are often suitable for fires, but forests do not always have enough fuel to burn. A classic example is ponderosa pine forests in the Southwest. Mature ponderosa pines develop thick bark that protects the trunk from fire and allows the trees to survive as long as their canopy does not catch on fire. Fires burn understory shrubs and grasses along with tree seedlings. Only a few seedlings survive to adulthood, creating open, park-like forests. Oddly, ponderosa pines are absent from the Greater Yellowstone Area, despite being found all over the West. However, Douglas-firs are found here, and they are somewhat similar to ponderosa pines. Fuel limited systems are able to burn as soon as enough material has built up to sustain a fire. Usually, they burn every few years to every few decades, noticeably more frequently than climate-limited systems, and they do not replace the stand.
What is different about current fires?
Two terms frequently come up when fires are in the news: climate change and fire suppression. Let’s first focus on climate change. Here in the Greater Yellowstone Area, we have already observed an increase in average temperatures, and this increase has been irrefutably linked to human emissions of greenhouse gases. Fire in the Greater Yellowstone Area has been limited by climate, but climate change is increasing the frequency of summers that are warm and dry enough for large fires to happen. This means that forests can burn much more often than they have historically. We have already observed this: in 1988, large parts of Yellowstone burned for the first time in over a century, the normal time period, but since then, some stands of trees that started growing after 1988 have already burned again. This is a problem because young trees do not produce enough seeds to successfully establish and regrow the next forest. As a result, scientists expect large areas that are currently forested to become a different ecosystem, for example a Douglas-fir woodland or a sagebrush steppe.
Fire suppression refers to human intervention that has limited fire in the past. While fire suppression was practiced in Yellowstone during the 20th century, it did not make a meaningful difference because the climate limited large fires. But fire suppression has made a meaningful difference in southwestern ponderosa pine forests, for example. In the absence of frequent fires, more trees survived into adulthood, creating uncharacteristically dense forests. When fire happens, it burns grasses and seedlings in the understory, but also burns adult trees in the overstory. Because ponderosa pines have not evolved with this kind of fire, they have no adaptations to regenerate afterwards. Management such as fuel reduction through carefully planned tree harvest can reduce the effects of fire, but because dense forests are normal in the historically cool climates of the Greater Yellowstone Area, thinning is not appropriate here.
Changes will occur in forests of the Greater Yellowstone Area. Forests may be limited to higher elevations, if seeds can disperse fast enough, while woodlands and sagebrush-grasslands will expand. For some animals, this means less habitat, while for others it means more. For some people, the loss of forest is concerning, while others may appreciate future scenery. Ecological change throughout the 21st century is nuanced, and humans play a key role in it.
If you would like to learn more, here are some helpful resources:
Native Americans know a lot about fire & used it historically to manage their environment. Native knowledge and scientific methods are unique, but complementary:
- From the Indian Country Times: “For tribes, ‘good fire’ a key to restoring nature and people”
- From the NPS: “Indigenous fire practices shape our land”
More about forests and fire:
- In Yellowstone, about Dr. Monica Turner’s work:
- In the Southwest:
- Generally:
More about climate change:
More about tree rings & lake sediment cores:
Even more about everything: identify reliable information: